Gas fireplaces of the type that simulate natural wood fires are well known. There are many different types and many different designs of these gas fireplaces, for example, "gas logs" and "gas inserts" are gas fireplace products which are designed to be installed into existing wood-burning fireplaces to convert them into gas fireplaces. Other types of gas fireplace products include "free-standing gas fireplaces", "wall mounting gas fireplaces" and "zero-clearance gas fireplaces". Such gas fireplaces may be conventionally vented, power-vented, direct vented or unvented. All of these gas fireplaces use some type of gas burner to produce the flames in conjunction with an arrangement of non-combustible fire logs and often non-combustible embers to simulate a natural wood fire.
However, most of these burner systems provide only a poor simulation of a natural wood fire. This is due in part to regional and national product approval standards that govern the manufacture and sale of gas fireplace products. In particular, most gas fireplaces are required to produce relatively low levels of carbon monoxide unlike their wood fireplace counterparts which are unrestricted in the amount of carbon monoxide that they can produce. The appearance of the fire itself is a very important factor in the saleability of a particular gas fireplace. Accordingly, many gas fireplace manufacturers, designers and inventors continue to develop new and improved methods and apparatus for making a gas fire that more closely resembles a natural wood fire and also meets or exceeds the required product approval standards.
One type of burner system that has enjoyed good sales and wide acceptance for producing an appealing gas fire is a type of pan burner referred to as a "sand-pan burner". This type of burner is very common and usually consists of a light gauge sheet metal pan with vertically inclined walls that house a gas supply tube with holes that are usually directed downward towards a non-combustible granular material such as silica sand or vermiculite placed in the pan to cover the tube. During operation gas percolates through the voids of this material and ignites when it reaches the surface in the presence of a flame. This pan is placed on the firebox floor with non-combustible fire logs supported above it usually on some type of a fireplace grate. In effect, some of the openings between the granules on the top surface of the non-combustible material became the burner gas ports. A problem with this type of burner is that it generally requires a larger volume of gas per hour to produce an attractive fire which precludes its uses in many enclosed type gas fireplace products where the combustion requirements are more limited. In addition, since the gas ports are not well defined and may in fact vary considerably, good flame control is difficult resulting in undesired flame contact with portions of the metal grate or non-combustible logs increasing the production of carbon monoxide.
More recent pan or tray type burners are disclosed in U.S. Pat. Nos 5,328,326 and 5,399,084. These burner designs have a metal top wall enclosing the pan with internal components to direct or restrict the flow of gas within the burner, with numerous gas ports punched or drilled in long rows along the front and rear edges of the burner with provisions for placing a long front log between these front and rear rows of gas ports generally covering the entire central area of the burner. Additional gas ports linking front and rear rows of ports run parallel to the side walls of the burner. These pan burners clearly define the location of each gas port and the resulting flames offer reproducible results that can meet product approval requirements. While there is the capability of increasing flame height and width the resulting flames are in straight lines along the outer edges of the burner resulting in fire that looks very linear and orderly and consequently a fire that does not closely resemble a natural wood fire.